Mechanisms of Binding and Abiotic Degradation of Sulfamethazine to Iron and Manganese Oxides.

Animal agriculture is becoming a significant source of antibiotics to the environment, primarily through the waste generated by concentrated animal feeding operations (CAFOs). Subtherapeutic levels of antibiotics are often administered to animals in such facilities, as disease can spread quickly due to high animal densities. Most antibiotics consumed by the animals are not absorbed or metabolized, passing through the animals chemically unchanged with the waste. Animal waste products from dairy CAFOs are often applied to agricultural land as a fertilizer, where residual antibiotics are introduced to the environment. The primary concern with environmental loading of antibiotics from dairy CAFOs is the potential for an increase in antibiotic resistance of pathogenic bacteria. Although antibiotics introduced into the environment have the potential to produce this harmful side effect, the behavior of these compounds in soil remains poorly understood. Lessening the development of antibiotic resistance by bacteria resulting from land application of dairy manure is contingent on understanding how these antibiotics bind or degrade in soil systems. Laboratory batch experiments with pure mineral phases such as Fe oxides and Mn oxides, including goethite and birnessite, are ongoing in order to determine the specific sorption mechanisms, reaction kinetics, and abiotic degradation pathways of sulfamethazine, an antibiotic common to animal agriculture. Fourier transform infrared (FTIR) spectroscopy is being conducted for molecular-based studies on specific binding and LC-MS/MS for the determination of degradation products. A fundamental understanding of how these common soil minerals bind and degrade antibiotics will aid in future studies with whole soil samples.